1. Field of the Invention
The present invention relates generally to personal audio devices such as wireless telephones that include noise cancellation, and more specifically, to a personal audio device in which the anti-noise signal is biased by filtering one or more of the adaptation inputs.
2. Background of the Invention
Wireless telephones, such as mobile/cellular telephones, cordless telephones, and other consumer audio devices, such as MP3 players and headphones or earbuds, are in widespread use. Performance of such devices with respect to intelligibility can be improved by providing noise canceling using a microphone to measure ambient acoustic events and then using signal processing to insert an anti-noise signal into the output of the device to cancel the ambient acoustic events.
The anti-noise signal can be generated using an adaptive filter that takes into account changes in the acoustic environment. However, adaptive noise canceling may cause an increase in apparent noise at certain frequencies due to the adaptive filter acting to decrease the amplitude of noise or other acoustic events at other frequencies, which may result in undesired behavior in a personal audio device.
Therefore, it would be desirable to provide a personal audio device, including a wireless telephone, that provides noise cancellation in a variable acoustic environment that can avoid problems associated with increasing apparent noise in some frequency bands while reducing apparent noise in others.